Adjustable shelf



FIG. 1 is a front perspective view of an adjustable shelf, showing my new design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof;

FIG. 7 is a top view thereof; and,

FIG. 8 is a bottom view thereof.

The broken lines in the drawings illustrate the portions of the adjustable shelf, which form no part of the claimed design. 

CLAIM The ornamental design for an adjustable shelf, as shown and described. 